Chase: Diffeiencesin diet of Thunnus thyninis at seasonal feeding grounds off New England 



179 



but they occur on a limited spatial scale in relation to At- 

 lantic herring in the (nilf of Maine, and changes in tlieir 

 population abundance are not well documented. Atlantic 

 herring and sand lance are also important in the diet 

 and distribution of marine mammals in the Gulf of Maine 

 (Payne et al., 1990; Weinrich et al., 1997; Gannon ct al., 

 1998). 



Changes in bluefin tuna stock composition and the long- 

 term impact of small-mesh trawling gear on commercially 

 important prey items (squid, silver hake, and butterfish) 

 in southern New England waters and Mid-Atlantic areas 

 where bluefin tuna catches have diminished are two poten- 

 tially confounding factors in this discussion. In the man- 

 agement of Atlantic bluefin tuna, care should be taken to 

 recognize that the fluctuations in the regional abundance 

 of this species can be influenced by more than changes in 

 stock structure. Changes in major prey populations, pro- 

 duced either by environmental features or by fishery prac- 

 tices, can have a profound effect on regional aggregations 

 of bluefin tuna. Investigations should be conducted on in- 

 troducing forage-base information into the interpretation 

 of catch-per-unit-of-effort indices of abundance for Atlan- 

 tic bluefin tuna populations. There is also a need for future 

 research to improve our knowledge on the bioenergetics 

 of this warm-bodied tuna and its associated relationships 

 with prey species. 



Acknowledgments 



This study was conducted by the Massachusetts Division 

 of Marine Fisheries (DMF), Commonwealth of Massachu- 

 setts, and funded by the Federal Aid in Sportfish Res- 

 toration Program. I would like to thank the DMF and 

 National Marine Fisheries Service staff who assisted with 

 field sampling and the technical review of this project. I 

 am especially thankful to Steve Cadrin for his review of 

 the manuscript and assistance with the statistical analy- 

 ses. I am very grateful to the many fishermen and tuna 

 buyers who contributed stomach samples and catch infor- 

 mation. Special thanks are due to the following for the 

 contribution of large numbers of samples: Bill Raymond, 

 Mark Godfrey, Rodman Sykes, and the crew of FV Debra 

 Lynn, Great Circle Fisheries, Ralboray, Crocker and Sons, 

 Canal Marine, and Atlantic Coast Fisheries. 



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